In liquid crystal display devices, an optical member such as a phase difference film is used for improving performance. When a phase difference film is used, for example, for antireflection of mobile devices, organic EL televisions and the like, as well as optical compensation of liquid crystal display devices, a slow axis of the phase difference film needs to be inclined at an angle neither in parallel nor perpendicular with respect to a transmission axis of a polarizer. On the other hand, a transmission axis of a polarizer is usually in parallel to a long-side direction or a short-side direction of a rectangular display surface of devices. Thus, a rectangular phase difference film having a slow axis in a diagonal direction with respect to a side thereof is demanded.
A phase difference film has hitherto been produced by longitudinal stretching or lateral stretching of a long-length pre-stretch film. In this description, longitudinal stretching refers to stretching of a long-length film in the lengthwise direction thereof, while lateral stretching refers to stretching of a long-length film in the width direction thereof. For obtaining a rectangular phase difference film having a slow axis in a diagonal direction from such a long-length film, the film needs to be diagonally cut out such that the side is inclined in a diagonal direction with respect to the width direction of the long-length film. However, with such a production method, the amount of disposed film increases and production of a film by a roll-to-roll process becomes difficult, and thus production efficiency is decreased. For addressing to this issue and improving production efficiency, it has been proposed to perform stretching of a long-length pre-stretch film in a diagonal direction (See Patent Literatures 1 to 4).